Scavenging of the cylinders of twostroke-cycle internal combustion engines



Feb, 6, 1949., w, LL 2,189,357

SCAVENGING OF THE CYLINDERS OF TWO-STROKE-CYCLE INTERNAL COMBUSTION ENGINES Filed July 12, 1959 2 Sheets-Sheet 1 9 7 5 sift? 1a :1 i g 1 1 g H} TJJETLLH Feia. 6, 194%. w CULL 2,189,357

SCAVENGING OF THE CYLINDERS OF TWO-STROKE-CYCLE INTERNAL COMBUS ON ENGINES Filed July 2 Sheets-Shet 2 9 //f III/It'll I/Ill] 1 1/11 v////////' 1/111; 'IIIIIII 5 a} a [1110 II l] v Patented Feb. 6 1940 ENGINES 1 2,189,357 "UNITED? S ATES {PATENT .omce I Q ew v "SCAVENGINGOF THE GYLINDERSOF TWO- STROKE-CYCLE COMBUSTION I William Cull, Shipley, England, assignor to Scott Motors (Saltaire) Limited, "Shipley; England Application .JulyilZ, 1939, Serial No. 284,060- In Great Britain February 23, 1938 This invention relates to tWOr-Stl'OkB-OYCIB internal combustion engines of vthe kind wherein a conical topped piston controls exhaustTports and transferports for combustible mixture compressed in the crank-case, andthe passages behind the transfer ports are so disposed that the entering streams of gases are dire'ctedwtangentially or radially with respect to the cylinder bore and transversely or with slight'or steep; upward inclination'with respect to the cylinderv axis.

The chief object of the presentinvention is to provide a new or improved construction of the cylinder of this .kind of twostroke-cycle engine wherein more accurate control of the gasesrluring the transferand exhaust periods is obtained so as to ensure more complete scavenging .of the exhaust gases,- and in consequence increased engine eificiency.

In two-stroke-cycle engines it has been proposed to employ a cylinder having three scavenging air ports on one side with exhaust ports on the oppositeside, the outer two ports directing scavenging air in streams up the admissionlside of the cylinder to the combustion end .of the latter, also; if desired, being deflected towards the cylinder Wall, and the centre air port serving to direct scavenging air across the cylinder to the exhaust so as, to clear the area :near the piston end. It has also been proposed to provide "a two stroke internal combustion engine with two scavenging ports arranged one .oneach side of the exhaust ports in such a manner that the issuing streams ofvscavenging air :are directed'to the cylinder wall opposite to the exhaust ports, the scavenging channels being inclined to a plane at right angles to the cylindergaxis and the ports as seen in plan being directed to a point outside the cylinder opposite to the exhaust ports.

According to the invention only three transfer portsare provided, one transfer port'is diametrically opposite to the exhaust port or ports-and the other two transfer ports are disposed symmetrically one on each side of the cylinder relative to the first port and are provided with leads :so that the piston, the angle which the passages behind the two further transfer ports make withthe-cylinder bore is such, that when seen in section transverse to the cylinder axis the lines of the side walls, when continued across the cylinder bore, strike the cylinder wall in points coincident with the side walls of the first mentioned transfer port. 55 In order that the inventionmay be clearlyunderstood and readily carried into effect, the same will now be more iully described with reference to and by the aid of the accompanying drawings, wherein:

60 Figure l is apart sectional elevation of a cylinthey are opened progressively by themovement of der of a two-stroke cycle internal-combustion o' rs n' Figure 2=is a sectional plan view taken along thehline A--A of Figural, butwiththe piston removed for the sake of clearness.

' Figure 3 is a part sectional elevation taken at "right angles to Figure .1. v

Figure tie a sectional planyiew taken along the lineB-B of Figure 3 "but withthe piston mately of the circumference of the -cyl-inder .bore. .Diametricall-y opposite to the exhaust port 4 is a transfer port .5 supplied by a-ztransfer, passage 5 leading from the crank case Ste-which the gases are supplied by an inlet portfi and two further-transfer :ports I are disposed equally on either side of the cylinder .3 relatively to the first or centrlztransfer port 5. Transfer passages 1, one of which is shown in :dotted lines in Figure 1, leads to each of the ports 1. The angle which the passages behind the two further transfer ports make with the cylinder bore is such that when seen section transverse 'to the cylinder axis, the lines of the .side walls, when continued across the cylinder bore, strike the cylinder wall in points coincident with the side walls of the :first-mentioned transfzergportili (seediigure 4').

In addition the passages behind the two further transfer ports 1 :areralso inclined upwardly and this upward :directien is at approximately the came angle ,as the conical piston crown 2. In a preferred construction, this :angle may be about 30 from the horizontal plane, which is at right angles to the vertical :axis :of the cylinder.

.The two further or tangential transfer ports 1 are provided with transverse upwardly inclined openings or leads as .at .8 so that they are opened progressively by the movement of the 'piston'l, the opening commencing at the exhaust port side. In this connection if desired, instead of leads being afforded by the tangential ports 1 such :leads may he formed by correspondingly shaping the-piston I so that the tangential ports 1 will open progressively commencing at the exhaust port side. .The first transfer port '5 diametrically opposite the exhaust :port :4 has no tangential controlof thewgases but the passage behind this port enters the cylinder at a greater angle than that which the passages behind the tangential ports Tl *makewith the horizontal plane which is atright angles to the vertical axis of the cylinder. In the preterred construction the angle which the passage behind the first transfer port 5"makes with the cylinder I would lie approximately between 57 and 63 to the said horizontal plane.

Thus it will be seen that as the piston moves from its upper compression stroke, as shown in dotted lines in Figure *1, downwardly in its working stroke, it uncovers the leads or openings 8 gradu This is clearly illustrated in Figure ally. wherein the lead 8 commences to open when the piston uncovers the top righthand corner thereof,

and as the piston descends the effective width of the opening increases until the piston uncovers the top lefthand corner, and upon further downward movement the opening will remain constant.

Owing to the leads or openings} givento the two tangential transfer ports, thetwostreams of gases emitted therefrom cross the piston top.

tangentially and unite as they commence to flow upwardly to the cylinder head 9 and behind the apex of the piston crown 2 towards the 'first port 5, whereupon said first port 5 opens and the united streams of gases are given an additional velocity by the gas issuing from the first port 5 just at a time when the initial velocity of said streams is falling, so that the gases are carried over the piston crown to the exhaust port side. In this connection the gases entering through the first port 5 pass through a Venturi throat in formed by restricting the area of the passage behind the said port 5 at a point immediately in advance of its opening into the cylinder I.

Thus it will be seen'that by giving the gases which are delivered by the tangential ports an additional velocity in an upward direction, more effective scavenging of the spent or exhaust gases is ensured with consequently increased engine efliciency.

I claim:

1. A combustion engine of the class described including a cylinder, a reciprocating piston mounted in the cylinder, said piston having a conical crown, an exhaust port leading from the cylinder, three transfer ports communicating with the cylinder, said ports being controlled by the movement of said piston, said cylinder having. three spaced vertically disposed transfer passages, each passage being inclined upwardly and communicating with one of the trans- :fer points, one of said transfer ports being dis- .posed diametrically opposite to the exhaust port and constituting a central transfer port, the two 'other ports forming tangential ports disposed one on each side of the central transfer port, means for progressively opening the tangential transfer ports upon the movement of the piston, and said tangential transfer ports facing the central transfer port sothat the issuing gas streams are projected across the cylinder to impinge upon the stream entering the cylinder from the central transfer port at approximately the same angle as the conical piston crown.

2. A two-stroke-cycle combustion engine of the class described including a cylinder, a reciprocating piston mounted in the cylinder, said piston having a conical crown, an exhaust port leading from the cylinder, three transfer ports communieating with the cylinder, said ports being controlled by the movement of said piston, said cylinder having three spaced vertically disposed transfer passages, each passage being inclined upwardly and communicating with one of the transfer ports, one of said transfer ports being disposed diametrically opposite to the exhaust port and constituting a central transfer port, the two other ports forming tangential ports disposed one on each side of the central transfer port, the two tangential transfer ports having upwardly transverse inclined openings communicating with the cylinder so that the tangential ports are progressively opened by the movement of the piston, and said tangential transfer ports facing the central transfer port so that the issuing gas streams are projected across the cylinder to impinge upon the stream entering the cylinder from the central transfer. port at approximately the same angle as the conical piston crown.

3. A two-stroke-cycle combustion engine of the class. described including a cylinder, a reciprocating'piston mounted in the cylinder, said piston having a conical crown, an exhaust port leading from the cylinder, three transfer ports communicating with the cylinder, said ports being controlled by the movement of said piston, said cylinder having three spaced vertically disposed transfer passages, each passage being inclined upwardly and communicating with one of the transfer ports, one of said transfer ports being disposed diametrically opposite to the exhaust port and constituting a central transfer port, the two other ports. forming tangential ports disposed one on each. side of the central transfer port, the two tangential transfer ports having upwardly trans- .verse inclined openings communicating with the cylinder so that these ports are progressively opened, by the movement of the piston, said tangential transfer ports facing the central trans fer port so that the issuing gas streams are projected across the cylinder to impinge upon the stream entering the cylinder from the central transfer port at approximately the same angle as the conical piston crown, and said central transi fer port having a Venturi throat formed by restricting the area of said passage at a point imme diately in advance of its opening into the cylinder.

4. A two-stroke-cycle combustion engine of the class described including a cylinder, a reciprocata ing piston mounted in the cylinder, said piston having a conical crown, an exhaust port leading from the cylinder, three transfer ports communicating with the cylinder, said ports being controlled by the movement of said piston, said cylinder having three spaced vertically disposed transfer passages, each passage being inclined upwardly and communicating with one of the transfer ports, one of said transfer ports being disposed diametrically opposite to the exhaust port and constituting a central transfer port, the two other ports forming tangential ports disposed one on each side of the central transfer port, the two tangential transfer ports having upwardly transverse inclined openings communicating with the cylinder so that these ports are progressively opened, by the movement of the piston, said tangential ports facing the central port, whereby the streams of gases emitted from the tangential ports cross the piston top tangentially and unite as they commence to flow upwardly to the cylinder head and when said central port opens the united streams of gases are given an additional velocity .by the gasissuing from the central port just at a time whenthe initial velocity of said streams is falling, the inclined passage of the central port entering the cylinder at approximately twice the angle which the passages communicating the tangential ports make with a horizontal plane disposed at right angles to the vertical axis of the cylinder.

' WILLIAM CULL, 

